Cathodic protection alloys



United States Patent 3,388,987 CATHODIC PROTECTION ALLOYS Ronald ErnestBailey, Ickenham, Uxbridge, England, as-

signor to The British Aluminium Company Limited, London, England, acompany of Great Britain N0 Drawing. Filed Oct. 12, 1965, Ser. No.495,321 Claims priority, application Great Britain, Oct. 21, 1964,42,969/ 64 4 Claims. (Cl. 75146) This invention relates to improvementsin cathodic protection alloys.

Various aluminum-base alloys have previously been proposed for use assacrificial anodes for the cathodic protection of metal structuresagainst corrosion by contact with sea water and related electrolytessuch as estuarine waters. One such alloy includes tin 0.01 to 2%, zinc0.5 to copper 0 to 0.015%, magnesium O to 0.05%, silicon 0 to 0.25%,iron 0 to 0.35%, titanium 0 to 0.01% and manganese 0 to 0.1%, the tinbeing dispersed throughout the alloy matrix, the balance being aluminumand inconsequential impurities. The aluminum used in the manufacture ofsuch an alloy would generally be 99.8% commercial purity aluminum andgallium would normally be present as an inconsequential impurity in theproportion of not more than 0.02%, being derived from the bauxite fromwhich the aluminum is produced. The tin would generally be dispersedthroughout the alloy matrix by a suitable form of heat treatment, thibeing desirable in order to avoid uneven attack and hence low efficiencyand to avoid undesirable variation in potential of the alloy when usedas a sacrificial anode.

It is to be understood that the percentages referred to in thisspecification are all by Weight.

In the prior proposal referred to above, the preferred upper limit fortitanium is set out as being 0.005%. We have found that, contrary toexpectation, the upper limit of 0.01% for titanium may be exceededwithout deleterious effect, and, indeed, certain advantages result fromsuch increased titanium content. Thus, the appearance of the casting isimproved Wherecast anodes are used, a more uniform structure of thealloy results which is beneficial to both cast and extruded anodes, andthere is also achieved a better contact with and minimising of voids atthe steel core of anodes cast from the alloy.

According to the present invention, there is provided for use as asacrificial anode material an aluminum base alloy including 0.5 to 10%zinc, 0.01 to 2% tin, 0 to 0.015% copper, 0 to 0.05% magnesium, 0 to0.25% silicon, 0 to 0.35% iron, 0 to 0.1% manganese and titanium inexcess of 0.01% but not more than 0.1%, the tin being dispersedthroughout the alloy matrix and the balance being aluminum andinconsequential impurities.

3,388,987 Patented June 18, 1968 ice Preferably, the titanium content ofthe alloy is in the range of from 0.02 to 0.06%.

An aluminum-base alloy material according to the present invention whichhas been found to be particularly useful has the following composition::

Percent Zinc 5.5 Tin 0.10 Iron 0.10 Silicon 0.10

0.04 Copper 0.005 Manganese 0.005 Magnesium 0.005

Balance aluminum and inconsequential impurities. The aluminum used was99.8% commercial purity. The tin was dispersed throughout the alloymatrix by a suitable heat treatment which involved heating the alloy for8 hours at 470 C. and quenching in water and with no artificial ageing.

The alloy had an efiiciency of 785% as measured by an impressed currenttechnique and a potential measured on the saturated Calomel scale of-1.100 v. The efficiency is defined for present purposes as the ratio ofthe metal dissolved in producing current to the total Weight of metaldissolved.

I claim:

1. An aluminum base alloy for use as a sacrificial anode materialconsisting essentially of 0.5 to 10% zinc, 0.01 to 2% tin, up to 0.015%copper, up to 0.05% magnesium, up to 0.25% silicon, up to 0.35% iron, upto 0.1% manganese and titanium in excess of 0.01% but not more than0.1%, the tin being dispersed throughout the alloy matrix and thebalance being aluminum and inconsequential impurities.

2. An alloy according to claim 1 wherein the titanium content is in therange of from 0.02 to 0.06%.

3. An aluminum base alloy for use as a sacrificial anode consistingessentially of 5.5% zinc, 0.10% tin, 0.10% iron, 0.10% silicon, 0.04%titanium, 0.005% copper, 0.005% manganese, 0.005% magnesium, the tinbeing dispersed throughout the alloy matrix, and the balance beingaluminum and inconsequential impurities.

4. An alloy according to claim 1 in which the aluminum is 99.8%commercial purity aluminum.

References Cited UNITED STATES PATENTS 3,321,305 5/1967 Hine -146 HYLANDBIZOT, Primary Examiner.

RICHARD O. DEAN, Examiner.

1. AN ALUMINUM BASE ALLOY FOR USE AS A SACRIFICIAL ANODE MATERIALCONSISTING ESSENTIALLY OF 0.5 TO 10% ZINC, 0.01 TO 2% TIN, UP TO 0.015%COPPER, UP TO 0.05% MAGNESIUM, UP TO 0.25% SILICON, UP 0.35% IRON, UP TO0.1% MAGANESE AND TITANIUM IN EXCESS OF 0.01% BUT NOT MORE THAN 0.1%,THE TIN BEING DISPERSED THROUGHOUT THE ALLOY MATRIX AND THE BALANCEBEING ALUMINUM AND INCONSEQUENTIAL IMPURITIES.